In a double boiler over medium-high heat, melt chopped chocolate and butter until smooth. Set aside to cool one minute.
In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt. Set aside.
At medium speed, combine sugar, eggs, and vanilla in the bowl of a stand mixer fitted with a paddle attachment. Once mixed thoroughly, slowly add chocolate and butter mixture, being sure chocolate mixture has cooled enough.
Reduce speed to low and gradually add flour mixture in three batches. Fold in mint chips by hand. Chill dough in the refrigerator at least 30 minutes before baking.
Using a 1 in. cookie scoop, place dough balls on a baking sheet lined with parchment or a silicone baking mat. Bake until cookies have sre still a little fluffy and cracked on top, about 15 minutes. Let cool on baking sheets on wire racks. Store at room temperature in an airtight container up to five days.